General Properties of Fungi

Sevtap Arikan, MD

FUNGUS• Widely distributed in nature (air,

water, soil, decaying organic debris)• ~400,000 types• Eukaryotic, highly developed cellular

structure• Facultatively anaerobic/strict aerobic• Chemotropic, nutrition: by

absorption• Nonphotosynthetic

Terminology

• Mykos: Fungus

•Mycoses: A disease caused by a fungus

• Mycology: Study of fungi

Major Developments in Mycology

• Increase in number of immunocompromised patients

• Newly developed antifungal drugs

• Antifungal susceptibility testing• Resistance to antifungal drugs

Fungi- Morphological Classification

• Yeast

• Mould

• Dimorphic

YEAST• Unicellular• Micr.: Oval to round (Dia: 3-15 µm)

Reproduce by budding Bud=Blastospore

Pseudohyphae • Macr.: Pasty colonies

(resemble bacteria)

MOULD

•MulticellularMicr.: Hypha(e) (dia: 2-10 µm)

SporesMacr.: Surface texture: Cottony/

wooly/ velvety/ granular...Pigmentation: observed

from the reverse

Mould-Definitions

•Hypha

•Mycelium: a. Vegetative b. Aerial

Classification of Hyphae

BASED ON:A. Existence of septa

Septate NonseptateB. Shape and Morphology Racquet Spiral

Nodular Root-like (rhizoid)

Pectinate Chandler

DIMORPHIC•Capable of growing in mould

or yeast form under different environmental conditions (temperature, CO2, nutrients)

•Thermal dimorphism (a group of pathogenic fungi)

Subcellular Structure of Fungi

• Capsule (present only in some fungi)• Cell wall• Cell membrane• Cytoplasm

Nucleus, nuclear membrane, nucleolus, ER, mitochondria,

vacuoles

CAPSULEStructure: Polysaccharide Functions: -Antiphagocytic

-Virulence factor

•Exist only in some fungiCryptococcus neoformans (encapsulated yeast)

CELL WALL• Antigenic in natureStructure: Multilayered

a. polysaccharides (~90%): hexose and hexosamine polymers b. proteins and glycoproteins (~10%)

Functions: Provides shape, rigidity, strength and protection from osmotic shock

Major polysaccharides of fungal cell wall

POLYMER MONOMERChitin N-acetyl glucosamineChitosan D-GlucosamineCellulose D-Glucose-Glucan D-Glucose-Glucan D-GlucoseMannan D-Mannose

• The type and amount of the polysaccharide vary from one fungal species to other.

CELLULAR MEMBRANEStructure: BilayeredPhospholipidsSterols (ergosterol, zymosterol)

Functions: a. Protects cytoplasmb. regulates the intake and secretion of

solutesc. facilitates capsule and cell wall

synthesis

FUNGAL SPORES

• Spores function in reproduction of fungi.

1. Sexual reproduction --Sexual spores

2. Asexual reproduction--Asexual spores

3. Parasexual reproduction--Genetic exchange

SEXUAL SPORES

1. Zygospore

2. Ascospore

3. Basidiospore

4. Oospore

ASEXUAL SPORES

1. Arthrospore2. Blastospore3. Chlamydospore4. Macroconidium5. Microconidium6. Sporangiospore

Fungi-Taxonomic classification

• Depends primarily on the type of sexual spore

Phylum -mycotaClass -mycetesOrder -alesFamily -ceaeGenusSpecies

Fungi-Taxonomic classification

SEXUAL SPORE CLASSZygospore----------ZygomycetesBasidiospore--------BasidiomycetesAscospore----------AscomycetesNone/Unknown---- Deuteromycetes

(“Fungi Imperfecti”)

MYCOSES

•Superficial (Hair, skin, nail, cornea)

•Subcutaneous•True systemic (endemic)•Opportunistic

LABORATORY DIAGNOSIS OF

MYCOSES• Direct microscopic examination

Gram, potassium hydroxide (KOH), calcofluor white, India ink

• Culture Sabouraud dextrose agar Mycobiotic agar

• Serology